Completed video and film programs are generally composed of segments from several sources. The programs are typically assembled by an editor who views the sources of material that are available and chooses the segments that will make up the final program. However, the program is not usually edited at the same place or time as the physical production of the final video tape or film; instead, the final production occurs at a facility equipped to produce the high-quality editing that is required for the final product. Therefore, the original editor of the program must generate a set of editing instructions to be used in the construction of the final program which is commonly automated using computer technology.
A set of editing instructions for video or film programs is often produced in a format called an edit decision list (EDL). A conventional EDL consists of a sequence of editing instructions, each of which is a computer instruction for a computerized edit controller which assembles a final program from source material. An editing instruction represents an event description, where each event is a transition to a new program segment. There are a number of available EDL formats (CMX, GVG, Sony, etc.), but each conveys similar information. The event description contains such information as the source of the new program segment, the time codes describing both the portion of the source that will be recorded and its destination in the final program, and the type of edited transition that is to be used from the previous segment. Using the information represented by editing instructions, the final program can be automatically constructed from the several sources of program material.
However, there are several problems with using conventional EDL's for video editing. Although EDL formats were created in a form which allowed them to be read by people, they are not in a form that is readily understood, as they are intended primarily to be computer instructions. A conventional EDL contains only alphanumerical information describing the video or film program transitions. This information is usually sufficient to produce the program. However, it is impossible from a conventional EDL to visualize the final program or its sources. For example, if an EDL requires modification, the original source material must be examined to determine the effects of any modification. This problem could arise, for instance, if an EDL was created to produce a sixty-minute program, but the appropriate program length was subsequently determined to be fifty-five minutes, thus requiring material to be cut. If the original editor (i.e., the person who produced the EDL) is unavailable or does not remember the exact nature of the segments of the program, it is impossible to determine from the EDL alone which portions of the program should be cut.
Furthermore, because the video or film program represented by the EDL cannot be readily visualized, in order to view the final program it must be actually constructed from the EDL. For example, if the final program is a television commercial, it is common to have it approved by the advertiser. Because the program represented by the EDL cannot be readily visualized, the final video tape or film must be sent to the advertiser for prior approval, which is an expensive and time-consuming process.